This study, conducted at six southern universities, analyzed the validity and reliability of a researcher developed instrument designed to evaluate educational software in secondary mathematics. The instrument called the Instrument for Software Evaluation for Educators uses measurement scales, presents a summary section of the evaluation, and provides recommendations for purchasing decisions. The study sample included 304 education students enrolled in graduate and undergraduate mathematics methods and computer education courses. The software was selected from commercial and public domain clearinghouses. A total of 52 packages were used on Apple and IBM personal computers. Content areas of the courseware included algebra, geometry, trigonometry, calculus, general mathematics, and statistics. Content, construct, and predictive validity as well as internal consistency and test-retest reliability of the evaluative instrument were investigated. Results indicate that the instrument has appropriate content validity, four stable constructs, and retest reliability. (TJH)